Human perception of sound is responsive of two types of vibrations: (a) air conducted vibrations; and (b) bone conducted vibrations.
Air conducted vibrations are picked up by the outer ear, and travel down the ear canal to the ear drum, where the vibration is converted into mechanical energy which passes into the middle ear, where the bones in this region, the malleus, incus, and stapes, receive this signal (wherein the stapes is covered in a fluid which acts as good transmitter between the bones of the middle ear and the inner ear). The signal is sent through the said fluid to the inner lining of the cochlea within the inner ear, wherein the cochlea is lined with minuscule hairs that extend back towards the auditory nerve. Some of the minuscule hairs become excited in response to the various frequencies of the signal, and the excitation creates an electrical impulse in the auditory nerve which is sent to the brain.
Bone conducted vibrations that are applied to the skull are converted to inner cranial vibrations, wherein it is noted that different parts of the skull offer different conductivity of such vibrations. In order for the sound to be percepted, it must be transduced into an electrical signal, thus, based on bone conducted hearing, the cranial vibrations directly stimulate the hairs of the cochlea, while bypassing the outer and middle ears completely (it is noted that since the skull itself vibrates, there is no need for an external receiver such as the pinnae to pick up the signal). Similarly to air conducted vibrations hearing, different minuscule hairs are excited in response to the frequency of the bone conducted vibrations, thus enabling the perception of different frequencies.
It is well known to any person skilled in the art that the conduction of sound waves through an aerial medium, as well as the detection of sound that is conducted in this manner, is very problematic in some situations.
Virtually in every environment, multitudinous sounds surround a user. In some environments, such as in parties with high volume amplifiers or in crowded locations, the environmental sounds are very powerful, whereas in other situations, less powerful environmental sound may actually trouble the user.
Significant ambient sound in the user's surroundings may cause the user a significant inconvenience. More over, it impedes both (a) the perception of requested sound by the user, whether the requested sound is in the user's surroundings or is provided to the user by a sound system, and (b) the detection of sound generated by the user, by a sound detecting system or a communication system.
These two difficulties present a considerable obstacle in the creation of an efficient two-way communication system that is suitable for noisy conditions. People who are in noisy environment, may use a headset that covers the ears to reduce the amount of undesired noise penetrating the external ear channel. Some use also special a headset that reduces the ambient noise electronically by using active noise cancellation techniques. Some simply try to reduce the noise by covering their ears with their hands.
Previous attempts to solve these problems by using bone conduction have withdrawn to what is known as ‘half duplex communication systems’, in which the user can either receive a requested audio signal, or transmit a user sound, but not simultaneously.
It is desirable to find reliable and simple means of communicating in noisy environments. It is further desirable to find reliable and simple means for stimulating a user's encompassing sound perception, by way of bone conduction.